Xerographic recording apparatus

ABSTRACT

A photosensitive element comprising a photoconductive light controlled storage layer and adjacent thereto a photoconductive multiplying layer which has an electric field placed across the two layers. The storage layer is exposed to uniform illumination and subsequently the multiplying layer is exposed to the image illumination. Following the cessation of exposure and removal of the charging field, the two layers are stripped apart and the storage layer developed by a conventional method.

Nov. 10, 1970 L, OFFE 3,539,255

XEROGRAPHIC RECORDING APPARATUS Filed Sept. 25. 1955 FIG.

[Q n? W /8 A TI {ff/2 FIG. 2 20g y I r/7 I j:

INVENTOR. F IG, 4 9 WILLIAM L.GOFFE WK-W AT TORNE) United States Patent 3,539,255 XEROGRAPHIC RECORDING APPARATUS William L. Golfe, Webster, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Sept. 23, 1966, Ser. No. 581,602 Int. Cl. G03g 5/00 U.S. Cl. 35516 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates in general to the art of xerography, and in particular, to a novel photosensitive element.

In the art of xerography, a xerographic plate containing a photoconductive insulating layer is first given a uniform electrostatic charge in order to sensitize its surface. The plate is then exposed to an image of activating electromagnetic radiation such as light, X-ray or the like which selectively dissipates the charge in the illuminated areas of the photoconductive insulator, while leaving behind a latent electrostatic image in the non-illuminated areas. The latent electrostatic image is then developed or made visible by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. This concept was originally disclosed by Carlson in US. Pat. 2,297,691, and is further amplified and described by many related patents in the field.

To a large extent vitreous selenium has become a standard photoconductor in commercial xerography. It has been discovered, however, that some of the limitations of vitreous selenium can be improved by the addition of allowing elements which enhance such properties as spectral response, light sensitivity, photoconductive stability, etc. U.S. Pats. 2,803,542 to Ullrich, and 2,822,300 to Mayer et al., both show the advantages of modifying vitreous selenium by the addition of appreciable amounts of arsenic in order to yield a broader range of spectral sensitivity, increase the overall photographic speed, and in general improve the stability of the photoconductive layer. In addition, US. Pat. 2,803,541 to Paris sets forth the advantage of added spectral response by the addition of tellurium to selenium to form a more panchromatic photoreceptor.

To a large extent commercial photoconductive layers are uniformly charged prior to image exposure through the use of a corona charging device such as that shown in US. Pat. 2,777,957 to Walkup.

In addition to the above named photoconductors, binder plates comprising an inorganic or organic photoconductor dispersed in a substantially insulating binder such as that shown in US. Pats. 3,121,006 and 3,121,007 to Middleton et al. also are illustrative of conventional photoconductive materials known to the art. Certain photoconductors, such as for example vitreous selenium overlaid with a thin layer of selenium-tellurium, cadmium sulfide, and others, although having generally good photosensitivity, show a high dark current or dark decay 'ice when used in the conventional xerographic mode. In addition, these and other photoconductors exhibit an undesirable high background.

It is, therefore, an object of this invention to provide an improved photosensitive element which overcomes the above noted disadvantages.

It is another object of this invention to provide a photosensitive element which has substantially no background.

It is another object of this invention to provide an imaging system utilizing high dark current photoconductors.

It is a further object of this invention in which conventional type charging methods may be eliminated.

It is yet another object of this invention to provide a novel photosensitive element. x

The foregoing objects and others are accomplished in accordance with this invention by providing a photosensitive device comprising a photoconductive light-controlled-storage layer employed adjacent to a photoconductive multiplying layer. To form an image, an electric field is placed across the sandwich formed by the two photosensitive layers, and the storage layer exposed to uniform illumination. The illumination on the storage layer is then removed from the storage layer simultaneously with the start of imagewise illumination of the multiplying layer, with the image illumination and field being then simultaneously removed, leaving a charge pattern on the aforementioned storage layer. The storage layer and multiplying layer are then stripped apart and the storage layer containing the charge pattern on its surface developed by any conventional technique.

Through the use of this technique, conventional type xerographic charging such as corona charging may be entirely eliminated, and in addition, it is possible to utilize high dark current photoconductors and operate them with quantum efliciencies above unity.

The advantages of the improved photosensitive storage layer will become apparent upon consideration of the following disclosure of the invention; especially when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic sectional view of one form of apparatus for carrying out the invention.

FIG. 2 is a schematic sectional view of the apparatus of FIG. 1 during exposure to imaging light.

FIG. 3 is a schematic sectional view of the storage layer portion of the apparatus of FIGS. 1 and 2.

FIG. 4 is a schematic sectional view of a second embodiment for carrying out the invention.

Referring to FIG. 1, reference character 10 designates a temporary sandwich configuration made up of a plate having a photoconductive multiplying layer and a separable storage layer overlaying said plate with a thin layer of charge transfer liquid disposed between said multiplying layer and said storage layer. The multiplying layer portion of said plate comprises a transparent backing 11 such as glass or plastic. Overlaying said transparent support member is a conductive base portion 12 comprising any suitable conductive substrate. Typical conductive substrates include metals such as copper iodide, aluminum, tin oxide, gold, and silver. The conducting layer over the transparent support member must be at least partially transparent, in order to allow light sources 19 and 20 to function effectively. Overlaying said conductive support is a photoconductive multiplying layer 13 which may comprise any suitable photoconductor. Typical photoconductors are: vitreous selenium, vitreous selenium undercoated with a more sensitive photoconductor such as an alloy of vitreous selenium and tellurium, and binder plate configurations such as those set forth in US. Pat. 3,121,006 to Middleton et al. Overlaying the multiplying ate) Union Carbide and Carbon Corporation. The thickness of the liquid between the sandwiching layers is not particularly critical and may conveniently range from about 0.2 to 1 micron in thickness.

The thickness of multiplying layer 13 generally falls within the range of conventional commercially used photoconductors which range from about to 50- microns in thickness, but may function at thicknesses greater or less than the above mentioned range.

Overlaying the charge transfer liquid is a light control storage layer which may consist of any conventional photoconductor such as vitreous selenium or a conventional photoconductor binder layer configuration such as that shown in the above mentioned patent to Middleton et al. This storage layer is in general thinner than the multiplying layer below and ranges in thickness from about /2 to 4 microns. The light control storage layer 15 is backed with a conductive backing 16 which may comprise any conductive member such as that used for conductive backing 12; A transparent backing sheet 17 is used in back of conductive member 16 and may comprise any material such as that used in backing member 11 described above. If desired, the transparent backing members 11 and 17, may be eliminated entirely. Electrical circuit 18 provides a potential between the conductive substrates 12 and 16. A source of illumination for uniform control light through the back of the light control storage layer 15 is provided at 1-9.

In FIG. 2 the same apparatus as shown in FIG. 1 is again shown with a light source 19 removed and imaging light source positioned below multiplying layer 13.

In FIG. 3 storage layer 15 is illustrated showing a developable electrostatic charge pattern shown on its surface.

The operation of the device shown in FIGS. 1, 2 and 3 will now be described in detail.

In FIG. 1 a constant potential system is shown with the potential and the uniform control light turned on. The positive charge transferred to the storage layer as a result of sweep out and displacement dark current is not stored because of the high photoconductivity of the storage layer. After the dark current has settled to an equilibrium value, and the multiplying mechanism has become fully operative, the control light is turned off simultaneously with the image light being turned on. This point in the sequence is illustrated by FIG. 2 wherein the image light now being turned on the storage layer is no longer illuminated and becomes a good insulator and stores the charge transferred to it. When the light exposure has been completed, the applied potential is removed, the storage layer is then separated from the multiplying layer as shown in FIG. 3. The stored electrostatic charge image shown in FIG. 3 is then developed by conventional technique well known to the art.

In a modification of the imaging procedure described, the control light is also on during the image-light exposure. The intensity of the control light is chosen so that the photocurrent through the storage layer is equal to the dark current through the multiplying layer. Consequently, only the charge transferred as a result of the image light exposure is stored. In a further embodiment of this invention, the structure of device shown in FIG. 1, the storage layer is attached with a blocking contact directly to the top of the multiplying layer. In this configuration the oil is used between the upper electrode and the storage layer. The resulting constant potential system is operated in a manner similar to that previously described. In a further embodiment, as shown in FIG. 4, a corotron 21 is used in place of the upper electrode and its oil contact to the storage layer. This corotron is so designed that a constant potential is maintained between the top electrode and the conducting substrate of the multiplying layer during the image light exposure. The operation of this system is similar to those described above.

In a further modification of this embodiment, the liquid oil transfer medium 14 as shown in FIG. 1 may be replaced by an air gap which may range in thickness from about 0 to 25 microns.

The following examples further specifically define the present invention with respect to a method of forming an electrostatic image using a light control charged storage layer in conjunction with a conventional photoconductive multiplying layer. The parts and percentages in the disclosure, examples, and claims are by weight unless otherwise indicated. The examples below are intended to illustrate the various preferred embodiments of carrying out a method of forming an image using a light controlled charge storage layer.

EXAMPLE I The device of FIG. 1 in the drawings consisting of an image forming multiplying photoconductor layer of selenium 25 microns thick on a 35% tellurium-selenium alloy 0.1 micron thick is provided on a NESA substrate. A inch glass base support is placed below the multiplying layer. A layer about /2 micron thick of 0.4% dibutyl tin dilaurate in 50 est. silicone liquid is placed between the multiplying photoconductor layer and an overlaying storage layer comprising a 4 micron thick layer of vitreous selenium having a backing of semi-transparent aluminum on Mylar 25 microns in thickness, and being further backed with a inch transparent glass plate. The device described above and as illustrated in FIG. 1 is imaged in the following manner: a potential of 400 volts is imposed on the circuit which connects the NESA and aluminized Mylar condutive coating. The NESA is maintained at a negative polarity. The potential is held at 400 volts, the voltage being pulsed for /2 to 1 second with the circuit simultaneously opening an exposure shutter which allows an imaging light source of 1260 foot lamberts through an f/S lens to contact the NESA plate supporting the selenium-tellurium photoconductor. The circuit is short circuited for /5 of a second after the voltage pulse is completed and the structure is then separated. A uniform control light supplying 1.5x 10* photons per second per cm. of 4000 angstrom light is maintained on during the entire light pulse which lasts for & of a second. After separating the sandwich configuration a resulting electrostatic image of volts is formed on the storage layer as measured with an electrometer probe. There is substantially zero background potential on the resulting stripped storage layer.

EXAMPLE II The stripped storage layer containing the electrostatic image is then developed by cascading said layer withelectroscopic marking particles. The image is then transferred to a sheet of paper and heat fused to form a permanent image having high quality and substantially no background.

EXAMPLE III selenium-tellurium multiplying layer. The voltage pulse is for a period of A of a second with the shutter being simultaneously open with the voltage pulse. The circuit is short circuited for 1 second after the voltage pulse. The storage layer of selenium is exposed to 7X10 photon seconds cm. of 4000 angstrom light during the entire voltage pulse which lasts for A of a second. This results in an electrostatic image of -60 volts on the storage layer with substantially zero background potential.

EXAMPLE IV The storage layer is then stripped away from the photoconductive layer and developed with electroscopic marking particles by the method set forth in Example II. This results in a high quality image having substantially no background.

Although specific components, proportions and procedures have been stated in the above description of a preferred embodiment of the novel imaging step employing a charged storage layer, other suitable materials, as listed above, may be used with similar results. In addition, other materials and procedures may be employed to synergize, enhance or otherwise modify the novel method and device described above.

Other modifications and ramifications of the present invention would appear to those skilled in the art upon reading of the disclosure. These are intended to be within the scope of the invention.

What is claimed is:

1. A light controlled imaging device comprising:

(a) a photoconductive multiplying layer overlaying a substantially transparent conductive support member;

(b) a photoconductive storage layer having a substantially transparent conductive support member positioned above said multiplying layer with said photoconductive layers contacting each other through (c) a thin layer of charge transfer liquid; and

(d) electrical means for inducing a potential between said conductive members; and

(e) uniform light control means located above said storage layer, and

(f) imaging light means located below said multiplying layer,

(g) said electrical means so connected as to control either or both light means simultaneously with the generation and termination of the voltage pulse with controls for suitable delays after the generation of the voltage pulse.

2. The device of claim 1 wherein insulating transparent backings are provided on each conductive substrate.

3. The device of claim 1 wherein a corotron is used in place of the conductive support for the storage layer and the charge transfer liquid is eliminated, with the storage layer being removably attached to the photoconductive multiplying layer.

4. The device of claim 1 wherein a charge transfer liquid is replaced with an air gap.

5. The device of claim 1 wherein the multiplying layer comprises a high dark current photoconductor.

6. The device of claim 5 wherein the photoconductor comprises a layer of selenium on a layer of seleniumtellurium alloy.

References Cited UNITED STATES PATENTS 3,383,993 5/1968 Yeh 35510X JOHN M. HORAN, Primary Examiner US. Cl. X.R. 

